The answer is A. The filament of an incandescent light bulb lights up, it is due to the resistance it creates towards the electric current flow in it. The resistance generates heat and hence the atoms become excited and vibrate with high kinetic energy. Some of the excited atoms lose the energy as photons to go back to a lower excited state, hence the light you see produced. There is, therefore, no chemical change in the filament, just physical change .
